The present invention relates to a stamping machine comprising a platen press.
It is known practice for texts and/or patterns to be printed by stamping, that is to say by using pressure to apply to a support in sheet form, colored or metalized film taken from one or more stamping strips commonly known as metalized strips. In the industry, such a transfer operation is usually performed using a vertical platen press into which the print supports are introduced, sheet by sheet, while the stamping strips are fed continuously.
In a standard platen press, stamping is performed between a fixed platen running horizontally, and a platen mounted so that it can move in a reciprocating vertical movement. Because this type of press is generally automated, conveyor means are provided to bring each sheet between the platens one by one. In practice, this is usually a series of gripper bars, each of which in turn grasps a sheet at its frontal edge, before pulling it in between the two platens of the press when the latter have been parted sufficiently.
A stamping strip is itself schematically made up of a backing strip of polyester type, to which a pigmented layer is secured by a layer of wax. The external face of this pigmented layer is itself coated with a coat of hot-melt adhesive. As in the case of the sheets, the feed of stamping strips to the press is conventionally automated, but in this instance by means of a drive system capable of unwinding each of said strips and feeding it in a clearly determined feed path which notably passes through the platen press. In general, such a strip drive system combines a series of turn bars which are installed along the entire feed path to guide the progress of the strips, with a number of feed shafts which are positioned downstream of said feed path in order respectively to drive the forward movement of each of said strips.
In industry, stamping is performed on specialist automatic machines. There are different types of machine construction, the most commonplace of which are vertical platen presses which work with a vertical reciprocating movement, cylinder presses and rotary presses.
The invention relates exclusively to the field of machines operating using a platen press. In these machines, the reciprocating movement is imparted to the moving platen by a set of members forming toggle joints and commonly known as toggle joints, collaborating with a drive mechanism of the crankshaft and connecting rod type. When the crankshaft describes a rotary movement, the toggle joints impart a reciprocating movement to the moving platen.
In these machines, the quality of the application depends on a number of parameters. The first is the stamping force. The stamping force is obtained through the vertical movement of the moving platen and the mechanism that moves it, by means of wedge bolts, with respect to a vertical position in which it lies flush with the surface of the fixed platen. A movement through a few tenths of a millimeter is enough to achieve precise adjustment of the stamping force, which may be considerable. Typically, this movement is of between one tenth of a millimeter and less than three millimeters.
The stamping force contributes to the uniform adhesion of the stamping foil to the substrate. If the stamping force is too low, the bond between the substrate and the applied foil will not be sufficiently resistant to scratching. It may even happen that the applied foil fails to adhere to the substrate, or even that there is no foil applied. Conversely, if the stamping force is too high, there is a risk that the stamping will be too deep, with damage to the substrate which may go so far as to tear it by cutting, or damage to the applied foil, or even both. For example, when using metalized strips, the brilliance of the lacquer over the applied foil is frequently lost when the stamping force is too high. Nonetheless, for users of these machines, the stamping force that the machine can tolerate is the most important feature of the machine.
Temperature is another crucial parameter in obtaining a good quality application. The temperature is generally between 90° C. and 130° C. and performs a dual role. Its first role is to soften the layer of wax that connects the layer or layers to be applied (for example a metalized layer and a layer of pigmented lacquer) to the polyester backing strip. The temperature therefore needs to be higher than the melting point of the wax. The second role of the temperature is to activate the adhesive layer that will bond the support and the applied strip together. Various formulations are suited to various supports. For example, for a support made of paper or of cardboard, the adhesive contains polymers compatible with cellulose. For a support made of polypropylene, it will be made up of polymers compatible with polypropylene. The greater the quantity of adhesive, the firmer the adhesive bond. By contrast, a smaller amount of adhesive means that the details of the stamping can be better defined. Too low a temperature will not perform these two functions. Conversely, too high a temperature may burn the strip or render the adhesive too runny and cause it to spill beyond the stamping region, impairing the quality of the periphery of the pattern.
In general, the higher the temperature and the higher the stamping force, the higher the production rate can be.
In order to achieve high production rates, these two parameters have therefore been gradually increased until the limits of the materials used have been reached. Thus, the rate is often limited only by the characteristics of the materials.
The technical problem that the subject of the present invention attempts to solve is that of proposing a stamping machine with a platen press which is able to achieve higher rates than the existing machines. The elements of the invention solve the technical problem. A stamping machine includes a platen press which has a fixed platen and an opposing moving platen effecting a reciprocating movement imparted by articulated members forming toggle joints. Each articulated member forming a toggle joint includes a connecting member which collaborates with a cam borne by a camshaft.
This description, which is given by way of nonlimiting example, is intended to provide a better understanding of the substance of the invention and of how it may be embodied. The description is also given with reference to the attached drawings, in which: